On a manufacturing line of electric resistance welded tube, a hydraulic pressure test is carried out to inspect quality of the manufactured electric resistance welded tube and especially quality of a welded part called a seam part. The hydraulic pressure test described here is carried out by pinching a predetermined length of manufactured electric resistance welded tube between a head stock and a tail stock disposed at front and back portions of a test line, sealing front and back opposite ends of the electric resistance welded tube, and injecting high-pressure water into the electric resistance welded tube through the head stock in this state. Pressure of the high-pressure water reaches about 90% of guaranteed strength and an electric resistance welded tube in which breakage of the welded part and a resultant burst of the tube do no occur is judged as a good-quality product in terms of mechanical strength.
With regard to a distinction between the head stock and the tail stock, a member for carrying out sealing of the tube end and injection and discharge of the high-pressure water is called a head stock and a member for carrying out sealing of the tube end and discharge of air in the tube is called a tail stock, in general. Both the stocks are movable in a front-back direction of the test line in order to conform to change in length of a tested tube and so that the tube end portions are inserted into both the stocks and sealed. Recently, the head stock for carrying out sealing of the tube end and injection and discharge of the high-pressure water is fixed and only the tail stock for carrying out sealing of the tube end and discharge of air in the tube is movable in some hydraulic pressure testers.
In such a hydraulic pressure tester for an electric resistance welded tube, fixing strength for resisting reaction force of the high-pressure water injected into the tested tube and fixed between the head stock for carrying out sealing of the tube end and injection and discharge of the high-pressure water and the tail stock for carrying out sealing of the tube end and discharge of air in the tube is required of both the stocks. Proposed from this point of view are an installed hydraulic pressure tester with both stocks firmly installed on a main frame, an embedded hydraulic pressure tester with both stocks embedded in a main frame, a coupled hydraulic pressure tester with both stocks coupled by tension beams, and the like.
These hydraulic testers have advantages and disadvantages. While the installed tester has an advantage that a space between both the stocks is open on upper and opposite sides to facilitate putting in and taking out of the tested tube, it has a disadvantage that, because both the stocks are cantilevered, a structure including the main frame is large and that a device is large in scale and weight. In the embedded tester, though the main frame can be made compact and lightweight, putting in and taking out of the tested tube are considerably restricted, because an open portion is formed only on an upper side. In the coupled tester, on the other hand, a tension rod can effectively receive a reaction force and therefore a device can be substantially reduced in scale and weight. Moreover, because a space between both the stocks is open on upper and opposite sides, a tested tube can be put in and taken out sideways and a tube carrier device for putting in and taking out the tube can be simplified.
In this coupled tester, however, a tube transfer mechanism between the tube carrier device for carrying the tested tube into and out of the test line between both the stocks and a tube clamping device for fixing the tested tube to the test line between both the stocks is inevitably complicated. In other words, when the tube carrier device carries the tested tube into the test line between both the stocks sideways, a tube support portion of the tube clamping device needs to be in a sufficiently lower position than a home position in the test line so as to avoid interference with the tested tube and the tube support portion needs to lift after the carry in to lift the tested tube to the test line. As a result, lifting and lowering strokes of the tube support portion become large to cause a problem of increase in size of the tube clamping device.
In addition, in the tube clamping device, clamp claws on opposite sides obstruct the carry in of the tube unless the clamp claws are fully opened to the opposite sides. Here, as the tube clamping device, a device having clamp claws which are opened and closed by utilizing lifting and lowering operations is preferable because of its simple structure (Patent Document 1). However, in such a tube clamping device, lifting and lowering strokes for opening and closing the clamp claws become large when the clamp claws on the opposite sides are fully opened and, as a result, the tube clamping device inevitably increases in size.